Method of depositing particulate layers



May 2, 1967 E. E. MAYAUD 3,317,319

METHOD OF DEPOSITING PARTICULATE LAYERSl Filed June 4, 1965 1 N VEN TOR. .a/7:1,l E Mmm/.0

,Niamey United States Patent C) 3,317,319 METHOD F DEPOSITING PARTICULATE LAYERS Edith E. Mayaud, Lancaster, Pa., assignor to Radio Corporation of America, a corporation of Delaware Filed .lune 4, 1963, Ser. No. 285,523 9 Claims. (Cl. 96-36.1)

This invention relates to the deposition of adherent, fine-textured layers of particles onto .a substrate and particularly to the making of mosaic-type phosphor screens for cathode ray tubes.

The invention may involve the use of techniques generally referred to 'as the direct photographic method. In such method all or part of a sensitized layer comprising a binder to which la sensitizing agent has been added for exposing to energy which will insolubilize the exposed portions thereof. The remaining portions, if any, are then removed by washing the layer in a sui-table solvent (developer). Particles of a desired kind, such as phosphor, are either incorporated into the sensitized layer prior to exposure or are added thereto 'after exposure.

Various photosensitizing agents, such as ythe dichromate salts, are not only capable of making a binder light sensitive, but also electron sensitive and heat sensitive. The term photographic as used herein, is therefore intended to include the use of any such suitable insolubilizing energy which can be suitably applied to the layer of the sensitized binder.

In one prior art version of the direct photographic method, a layer of slurry comprising water, particles, binder and sensitizer is applied to a substrate, dried, exposed, and developed. This method is one of several which many be termed presensitized methods, because the binder is already sensitized when applied to a sub strate. This method has lthe sometimes objectionable feature that the sensitizer may cause particles in the slurry to aggregate, thus preventing the obtaining of a fine textured layer of particles.

In a second prior ant version of the direct photographic method, a layer of pre-sensitized binder solution is applied to a substrate, dried, and exposed to make it tacky. Particles are then applied on top of the tacky surface and the layer is developed. Alternatively, the layer may be developed and then lthe particles applied to the tacky areas. This method sometimes has the objectionable features of poor wash-oit (development) of unexposed areas, non-uniform tackiness, and hence, nonuniform particle deposition across elemental exposed areas, low maximum obtainable thickness of particle deposition, and in some cases, coarse resulting texture due to the tacky surface attracting principally aggregates of particles.

In a third prior art version 4of the direct photographic method, a layer of particles ina silicate binder is settled onto a substrate .and the liquid settling pool poured off. The layer yis then treated with a pre-sensitized binder, dried, exposed. -and developed. This method has the objectionable feature that a binder (e.g., the silicate) is required which is in addition to the sensitized binder used in the exposing step, and which is ordinarily not removable from the Iiinshed -layer by high temperature bake-out. Moreover, the Vattendant disadvantages of a settling process such as aggregation ofthe settled particles are present.

It is therefore an object of this invention to provide a new and improved method of photographically de positing adherent l-ayers of particles onto a substrate.

lIt is also an object of this invention to provide a method of depositing tine textured particulate layers onto a substrate.

ICC

According to this invention, a layer comprising highly dispersed particles in a solution of an unsensitized binder is applied to a substrate. The l-ayer is then treated with a sensitizer to sensitize the binder thereof. Portions of the layer are then exposed to a suitable insolubilizing energy to insolubilize those portions. The layer may then be developed t-o remove the unexposed portions, if any. Because the binder is sensitized after it has been applied to the substrate, the method of this invention may 'be termed .a post-sensitization method.

The subject invention may be used in a variety of ways. For example, the invention may be used for: (a) depositing a mosaic pattern of color emitting phosphor particles for a color cathode ray tube onto a glass substrate; (b) depositing strips of UV emitting phosphor or secondary electron-emitting particles onto an aluminum subst-rate for generating indexing feedback signals to control the scan in a color cathode ray tube; (c) depositing a mosaic pattern of nonluminescent, opaque particles such -as carbon onto a phosphor screen of a color cathode ray tube; and (d) depositing a continuous, non-patterned phosphor layer onto a glass, aluminum or phosphor substrate of a cathode ray tube.

The single sheet of drawing is a diagram of steps which may be used in the practice of this invention as described below.

A slurry comprising a suspension of selected particles in a solution of unsensitized binder is rst prepared. For example, the particles may comprise phosphor or carbon particles, the binder may comprise polyvinyl alcohol (PVA), and the solvent of the binder solution may comprise water.

The polyvinyl alcohol (or other) binder included in this suspension slurry is one which can -be treated with a sensitizing agent to make the binder such that it will bec-ome insoluble on exposure to a suitable insolubilizing form of energy such as ultra violet or heat radiations or electron bombardment. The binder is, however, -at this stage of the process, not yet sensitized by the addition of a sensitizer.

The ratio of particles/binder/solvent in the slurry, while not critical, is preferably made within a specific range to facilitate application to a substrate, 4and to obtain good adherence to the substrate and subsequent insolubilization of the binder. In the case of slurries of phosphor, polyvinyl alcohol, and water, compositions comprising 3-30 weight pa-rts of phosphor, 0.3-30 weight parts of PVA, and 70-97 weight parts of water have been found to be satisfactory. -In the case of slurries of PVA, water, and graphite or carbon, compositions comprising 0.2 weight part of graphite, 0.2-0.5 weight part of PVA, and 99 weight parts of water have been found to be satisfactory.

The particles from which the desired layer is to be formed are preferably highly dispersed in the suspension so as to avoid any significant amount of particle aggregation. This results in the subsequently deposited particulate layer being of a desirably tine texture. If necessary or desired, a suitable dispersant, according to known practices, may be added to the suspension to insure a high degree of dispersion. For example, in the case of a hydrophobic phosphor such as zinc sulde or lanthanum phosphate, a small percentage (e.g. 0.4 weight percent of the suspension) of a strongly anionic dispersant such as a sodium lignin sulfonate may be added to the suspension. In the case of a calcium magnesium silicate phosphor, a high degree of dispersion may be obtained by milling the phosphor with a small percentage (eg. 0.5 weight percent of the suspension) of zinc oxide and a trace (eg. 0.03 weight percent of the suspension) of ammonia. Particulate material such .as hydrophilic silicate phosphors are best dispersed 'without any dispersant other than the polyvinyl alcohol solution itself.

The prepared slurry may be adjusted to a desired viscosity such as by the addition of more of the binder solution. A quantity of the slurry is then deposited upon a suitable substrate and spread thereover into a layer of desired thickness. The spreading, may, for example, be accomplished by spinning and tilting the substrate.

The layer of slurry is then dried without completely dehydrating or decomposing the binder. This may be accomplished, for example, by heating with infrared radiations, by warming in an oven, or by simply permitting the slurry layer to air dry at room temperature. The desired amount of drying of the screen can be determined by visual inspection. As water is removed from the wet slurry layer during drying, the layer begins to take on a dull or dry-looking appearance. When this appearance has spread substantially completely over the screen, the drying heat is removed. Further drying, while not changing the visible appearance of the screen, mayiundesirably drive out additional water and cause the screen to be dehydrated. When dehydration occurs, satisfactory subsequent processing of the screen may be diicult.

The dried layer is then treated with a suitable bindersensitizing solution to render the binder sensitive to exposure to a selected energy. The sensitizing solution may, for example, comprise a solution of a dichromate salt such as ammonium dichromate or potassium dichromate. The solvent in which the sensitizing agent is dissolved should be one which will not excessively dissolve the binder of the dried slurry layer when applied thereto. Solvents such as mixtures of acetone and water or alcohol and water are suitable when ammonium dichromate is used as the sensitizing agent and polyvinyl alcohol is used as the binder.

The sensitizing solution may be applied to the dried slurry layer such as by ilowing, spraying, or fogging it over the layer. Such application of the sensitizing solution serves to sensitize the binder of the layer without disturbing the deaggregated particle deposit.

The sensitized layer may then be rinsed in pure alcohol or acetone or equivalent to remove all excess dichromate which has not been absorbed by the binder. The sensitized layer is then dried in a manner, eg., similar to the preceding drying step.

All or part of the now-sensitized phosphor-binder layer is exposed to energy `which causes the sensitized binder of the layer to become insoluble. Where a dichromate sensitizing agent is employed, the exposure may, for example, be to UV light, electron bombardment, or heat. This energy exposure may be applied to the layer either as a pattern of discrete areas or by flooding the entire layer. For example, a pattern exposure may be made by projecting UV light through a suitable apertured stencil, or by scanning an intensity-modulated electron beam over the sensitized layer. A ood exposure may be made by heating the sensitized layer in an oven, or by irradiating it with infra-red.

The exposed layer is then developed by washing it with a suitable solvent. The solvent may be the same kind as that which was used in the slurry. In the case of a PVA binder, water is a satisfactory developer. The developing of the exposed layer may be performed by spraying the developer onto the layer or by otherwise ushing the layer with the developer. The temperature of the developer should be such that it easily dissolves the unexposed binder without adversely affecting the exposed insoluble areas of the layer. A water temperature of 20 C.-l00 C. has been found suitable for developing a layer having a PVA binder. Steam has also been satis- 'factorily used as a developer.

If during exposure, all portions of the layer were exposed and insolubilized, it may not be necessary to include 'a developing step, since there will be no unexposed soluble deposits to be removed.

Various measures may be taken to ensure good washol' (development) of the unexposed portions of the layer. For example, a solution of sensitized binder may or may not be applied to the substrate prior to application of the slurry thereto so as to provide a substrate surface which will not readily adsorb particles from the subsequently .applied slurry. Alternatively, the slurry itself may be adjusted to a desired pH so as to neutralize or minimize an adsorptive action between the slurry and substrate.

Specific examples of the invention are set forth below.

Example 1 An array of tine textured lanthanum phosphate strips are provided as follows: n

A 200 gram quantity of lanthanum phosphate phosphor, 0.40 gram of Marasperse N, a sodium lignin sulfonate marketed by Marathon Co., and 300 grams of water are milled at 120 r.p.m. for two days in a quart jar 80% filled with 6 mm. flint glass beads. A 20 gram quantity of a 10% aqueous solution of PVA (e.g. du Pont de Nemours Co. Elvanol type 52-22) is added to the milling jar and the entire quantity is milled for an additional hour. The stock is then drained from the jar. The jar is rinsed with 100 ml. of water which together with the stock is then filtered through miracloth and added to an additional 380 grams of 10% aqueous solution of PVA. This produces a slurry of phosphor particles having a PVA/ phosphor ratio of 0.20.

A quantity of the slurry is then applied to an aluminum substrate such as an aluminized phosphor layer and spread thereover -by spinning and tilting the substrate to provide a layer of from 0.05 to 2.0 mg. per square cm. The slurry layer is then dried by infrared radiations which produce a temperature of 25 C.-50 C. at the layer surface.

A binder sensitizer solution is then separately prepared by mixing l0 ml. of 10% aqueous ammonium dichromate with ml. of No. 30 ethanol. The sensitizing solution is then applied to the phosphor layer such as by spraying or ooding the layer therewith for about one minute. Since the solvent of the sensitizing solution is primarily alcohol, there is little dissolution of the PVA binder of the phosphor layer. The particle arrangement of the phosphor layer is therefore not adversely disturbed.

The sensitized phosphor layer is dried in air at room temperature. The dried sensitized layer is exposed for two minutes to a pattern of mil wide lines of ultra-violet radiation such as that produced by directing the rays of a General Electric Company type BH6 l kilowatt high pressure mercury arc lamp through a suitable stencil. Energy from the lamp is collected by a collimator whose ip is positioned approximately 75 cm. from the phosphor ayer.

The exposed phosphor layer is then developed by subjecting it to a water spray from a No. SS3 single nozzle at 20-40 pounds pressure for approximately two minutes.

The developed phosphor layer is then dried in air at room temperature.

Example 2 An array of fine textured carbon strips on a tine textured layer of lanthanum phosphate phosphor is provided tlm an aluminized color phosphor mosaic screen as folows:

A faceplate is provided with a mosaic screen comprising parallel strips of different color emitting phosphors using known phosphor deposition techniques. The mosaic screen is filmed with an organic heat-removable material and aluminized also according to known techniques. The aluminized screen is then soaked, for tive minutes, in Water, rinsed ot for 30 seconds with a No. SS3 single nozzle water spray at 20 pounds pressure and dried with infrared radiations for four minutes on a rotating turntable.

A three percent aqueous solution of PVA is applied over lthe aluminized screen using a slurry spinning and tilting procedure. The PVA coating is then dried for four minutes at a distance of approximately eight inches fro-m an 8-Calrod heating unit. The PVA coated screen is then washed by spraying with the No. SSS single nozzle for two minutes, and is then again dried with the 8-Calrod heating unit.

A slurry is prepared which comprises equal weight parts `of lanthanum phosphate phosphor and PVA with sufliicient water to provide a viscosity of 27 cps. A 0.5% quantity of Marasperse N is added to the slurry to provide good dispersion of the phosphor particles. The phosphor slurry is then applied over the PVA coated aluminized screen by a spinning and tilting slurry application cycle to provide a phosphor layer thickness of about 0.25 mg./cm.2. The slurry layer is then dried for four minutes at a distance of Veight inches from the 8- Calrod unit.

A photosensitizing solution is prepared which comprises one percent ammonium dichromate dissolved in a solvent of nine parts No. 30 ethanol alcohol and one part water. 'Ihe dried lanthanum phosphate phosphor layer is then photosensitized by sloshing 200 ml. of the ammonium dichromate sensitizer thereover for about 30 seconds. The excess sensitizer solution is drained from the screen for a few seconds. The screen is then immediately rinsed with 200 ml. of No. 30 ethanol for fifteen seconds. The screen is then again drained and dried with a high pressure air hose.

The sensitized lanthanum phosphate phosphor layer is then flood exposed by UV radiation for ten minutes with apparatus similar to that described in Example l.

A PVA coating is then applied to the lanthanum phosphate phosphor layer in a manner similar to the application of the PVA coating to the aluminized screen described above in this example. A graphite slurry is prepared by dispersing two parts electrolytic graphite (particle sizes below 0.5 micron) and one part PVA together with enough water to provide a viscosity of 7 cps. Also included in the graphite slurry is seven weight percent of ammonyx T, a cationic dispersent marketed by Onyx Chemical Corporation, and seven Weight percent Triton X-lOO, a non-ionic wetting agent marketed by Rohm and Haas Corp.

The graphite slurry is applied over the lanthanum phosphate phosphor layer by a spinning and tilting cycle and then dried at a distance of eight inches from the 8Calrod unit to the point at which the graphite begins to get dull in the center of the screen. The graphite slurry layer is then allowed to complete its drying by spinning in air without any heat being applied.

The dried graphite layer is then photosensitized in a manner similar -to the photosensitization of the lanthanum phosphate phosphor layer described above in this example.

'I'he screen bearing faceplate is then sealed in a chamber which is then evacuated. The sensitized graphite layer is then exposed for fteen minutes by bombardment with an electron beam of six micro amperes at 35 kilo- Volts. The spot size of -the electron beam is adjusted to produce a 90 mil exposure strip.

The exposed screen is then removed from the chamber and developed with water spray for two minutes at 40 pounds pressure using the No. SS3 single nozzle. The screen is then dried by infrared radiation.

Example 3 A suitable aluminized mosaic screen such as that described in Example 2 is provided as a foundation for an array of fine-textured strips of non-aggregated lanthanum phosphate phosphor particles which are applied thereto as described below.

The aluminized screen is water soaked, rinsed, dried, and precoated with PVA as described in Example 2, ex-

cept that -a 1.5 percent PVA solution is used and the drying thereof is at a distance of six inches from a 6-Calrod heating unit.

A lanthanum phosphate phosphor slurry is then prepared and applied to the PVA precoating as described in Example 2, except that the slurry also contains 0.1 percent Triton X-100 as a wetting agent.

The lanthanum phosphate phosphor layer is then sensitized, exposed, and developed in a manner similar to the photosensitization, the exposure, and the development of the graphite layer -as described in Example 2.

Example 4 Fine-textured dot deposits of non-aggregated red-emitting particles for a 21FBP22 shadow mask color cathode ray tube are laid down as described below.

A slurry containing water, PVA, and red emitting silver activated zinc cadmium-sulfide phosphor is prepared which has a PVA/phosphor ratio of 0.222. Suicient quantity of the slurry is applied to a faceplate panel to produce a screen weight of 2.5 mg./cm.2.

The slurry layer is dried and sensitized as described in Example 2, except that the solvent of the photosensitizer comprises nine parts acetone and one part water.

The sensitized phosphor layer is then exposed to UV radiation in a suitable dot pattern for from 8 to 24 minutes with apparatus similar to that described in vExample l.

Development of the exposed screen is in accordance with the procedure described in Example 1.

If desired other color-emitting phosphors, e.g. blue and green, of the same screen may be laid down using a similar post-sensitization procedure. The slurry composition and exposure schedule of the other phosphors may vary depending upon the phosphor itself Iand the structural nature of the deposition desired.

Because of the fine texture of layers which can be deposited by the post-sensitized method such as described above, the method is especially suited for providing particulate signal strips on the back of a color screen of elemental phosphor lines for use as electron pervious indexing. Such indexing strips made by using the post-sensitization method are highly nonporous (i.e., densely packed) and thus produce a minimum of signal noise. Yet they are quite thin so as to be highly electron pervious. For example, phosphor strip deposits have been provided by this invention with coverage (i.e. where the 'interstitial space between phosphor particles is only one-nineteenth the space covered by the particles) and yet -as thin as 0.06 mg./cm.2. Such phosphor strips absorb only 3% of the impinging electron beam energy. By contrast, phosphor strips deposited using pre-sensitized prior art techniques have given only 50% coverage at thicknesses as great as 0.10 mg. per cm.2 and have absorlbed as much as 10% of the energy of the impinging electron beam.

on the control of other ingredients such as slurry solvent, dispersants, and binders. It has been found that the percent of solvent (eg. water) in the slurry is one of the nature of water has a coagulating effect on hydrophobic particles such as lanthanum phosphate phosphor. It is therefore desirable to make such hydrophobic particles hydrophilic and polar by adsorption of a surface active dispersant which will give the particles a negative charge. Marasperse N, a strongly anionic sodium lignin sulfonate, has proved to be quite effective., Dilution of the slurry with a non-ionic type acrylic emulsion rather than with pure water is also helpful in achieving good dispersion in the slurry. One suitable acrylic emulsion is that 7 4available from Rohm and Haas Company as Rhoplex C72. This acrylic resin is believed to be primarily ethyl acrylate.

Where Maraperse N is used as a dispersant for lanthanum phosphate phosphor, at 0.4% Marasperse N and above, the lanthanum phosphate dispersion is stable. A concentration of about 0.5% of Marasperse N is preferred in dispersing lanthanum phosphate in aqueous PVA solution. l

The influence of the PVA/phosphor ratio on the state of aggregation and on the packi-ng of the resulting phosphor layer is minor compared to that of Marasperse N and water. Neither a high PVA/ phosphor ratio nor high viscosity are completely satisfactory in -overcoming the deleterious effect of insuicient dispersant. At low viscosities, a high PVA/ phosphor ratio does not prevent the coagulating effect of water on a phosphor slurry which contains insufficient dispersant.

The smoothness and packing of phosphor layers are excellent whenever they are layed down from a slurry in a good state of dispersion. This holds true even when the layers are applied from a slurry having a very high viscosity and with a high centrifugal spin spreading force. When a poorly dispersed slurry containing aggregation and lumps is applied at low spin spreading speed, the phosphor layer has poor packing and is rough. When the same slurry is applied at high spin spreading speeds, the greater stresses make the roughness and surface defects more pronounced.

Factors which influence the post-sensitization step include: the amount of water in the sensitizer solvent, the amount of sensitizer in the sensitizing solution, and the choice of solvent. The time duration of sensitization does not appear to be critical; times of from 30 seconds to 30 minutes have been satisfactorily used. In cases where a yPVA binder is used in the slurry and more than 20% water is included in the sensitizer solvent, the dried phosphor layers to which the sensitizer solution is applied are reswollen and made tacky and non-uniform. When less than about water by volume is included in the solvent, it is difficult to incorporate sufficient amounts of dichromate salts in the sensitizing solution to impart good sensitivity to the PVA of the particulate layer. The optimum concentration of water in either acetone or alcohol is from 10 to 20 percent by volume.

A 2 percent concentration of ammonium dichromate sensitizer in a 4:1 acetone-water solvent gives sensitivity equal to that of conventional pre-sensitized layers. Increasing the dichromate to 4 percent in the solvent mixture does not lessen exposure time measurably and only results in manipulation difficulties due to salting out of insoluble dichromate salts. y

A variety of different organic solvents are suitable tor use in preparation of the sensitiziug solution. Such solvents include i-proply alcohol, acetone, methanol, and No. 30 ethanol. Acetone, as well as other ketones, ibeing less susceptible to attack by oxidizing agents than are the alcohols, is preferred because of its stability in the presence of dichromate salts. Mixtures of acetone and dichromate salts in water have proved to be stable for more than sixteen hour-s. Furthermore, acetone has given somewhat better sensitivity and resulting shorter exposure times with UV light than sensitizing solutions made with ethanol. The alcohols, on the other hand, are preferred in those cases where the screen structure includes acrylic resin solids since such resins soften and become tacky in acetone.

Unsensitized lanthanum phosphate layers in PVA have been treated with dichromate sensitizing reagents for times varying from thirty seconds to thirty minutes. Line patterns have then been UV (ultraviolet) exposed in an exposure time series and developed. Data from these examples indicated that a thirty second treatment with a dichromate is as effective as a thirty minute treatmen in rendering the layers photosensitive to UV radiations. Moreover these post-sensitized proved to be equal in photosensitivity to layers.

What is claimed is:

1. The method of depositing a layer of particles onto a substrate comprising the steps of:

(a) applying to` said substrate a layer of a mixture including said particles and a binder which is solu- .ble in water (b) applying to said layer a solution of sensitizer for said binder, the solvent of said sensitizer solution comprising water and at Ileast one member of the group consisting of alcohol and acetone, thereby sensitizing said layer so that it will become insoluble in water when exposed to a given kind of energy, and then (c) exposing at least a portion of said sensitized layer to said given kind of energy.

2. The method of applying a phosphor deposit to a substrate comprising the steps of:

(a) depositing a layer of a mixture of deaggregated phosphor particles and polyvinyl alcohol binder onto said substrate,

(b) applying to said layer a solution of a sensitizer f for said binder, the solvent of said sensitizer solution consisting essentially of a minor proportion of water and a major proportion of at least one member of the group consisting of alcohol 'and acetone,

(c) exposing a portion of said sensitized layer to an energy which insolubilizes said binder, and

(d) developing the exposed layer.

3. The method of making a phosphor screen comprising the steps of:

(a) depositing on a substrate a layer of slurry containing phosphor particles, polyvinwl alcohol binder, and water;

(b) drying the slurry layer;

(c) applying to the dry slurry layer a solution of a dichromate, the solvent of said dichromate solution consisting essentially of about 10 to 20 volume percent water and about to 80 volume percent of at least one solvent from the group consisting of alcohol and acetone;

(d) drying the dichromated slurry layer;

(e) exposing the dichromated slurry layer to a pattern of actinic rays; and

(t) developing the layer to remove the unexposed portions thereof.

4. The method of providing a patterned layer of particles on a substrate, said method comprising the steps off:

(a) depositing onto said substrate a layer of a highly dispersed suspension of said particles in a solution of a binder which is soluble in water,

(b) drying said layer,

(c) treating said layer with a sensitizing solution, the

solvent of said sensitizing solution consisting essentially of about 10 to 20 volume percent water and the balance of at least one solvent of the group consisting of alcohol and acetone, said treatment enabling said binder to be made insoluble in water by subsequent exposure to a given type of energy,

(d) drying said treated layer,

(e) projecting energy of said given type onto portions of said layer to expose and render the binder of said portions insoluble in water, and

(f) developing said layer in water to remove any portions thereof from said substrate whose binder has not been insolubilized.

5. The method of provid-ing a patterned layer of particles on a substrate, said method comprising the steps of:

(a) depositing onto said substrate a layer of a highly dispersed suspension of particles selected from the group consisting of phosphor and carbon in an aqueous solution of polyvinyl alcohol binder,

(b) drying said layer,

layers have pre-sensitized (c) treating said layer with a sensitizng solution cornprising a dichromate salt, the solvent of said sensitizing solution consisting essentially of about 10 to volume percent Water and about 80 to 90 volume percent of a liquid selected from the group consisting of acetone and alcohol, said treatment enabling said binder to be made water insoluble by subsequent exposure to a given type of energy,

(d) drying said treated layer, l

(e) projecting onto portions of said layer said given type of energy selected from the group consisting of ultra-violet radiations, electron bombardment, and heat to render the binder of said portions Water insoluble, and

(i) developing said layer in Water to remove any portions thereof from said substrate whose PVA has not been Water insolublized.-

6. The method of providing a patterned layer of parti- :les on a substrate, said method comprising the steps of:

(a) depositing on said substrate a layer of a highly dispersed suspension of carbon particles in an aqueous solution of polyvinyl alcohol binder,

(b) drying said layer,

(c) treating said layer with a sensitizng solution comprising a dichromate salt, the solvent of said sensitising solution consisting essentially of about 10 to 20 volume percent water and the balance of a liquid selected from the group consisting of acetone isopropyl alcohol, methyl alcohol and ethyl alcohol, said treatment enabling said binder to be made water insoluble by subsequent electron bombardment,

(d) drying said treated layer,

(e) projecting electrons onto render the binder of said and (f) developing said layer in water to remove any portions thereof from said substrate whose binder has not been water insolublized.A

7. The method of providing a patterned layer of particles on a substrate, said method comprising the steps of:

(a) depositing on said substrate a layer of a highly dispersed suspension of phosphor particles in an aqueous solution of polyvinyl alcohol binder,

(b) drying said layer,

(c) treating sid layer with a sensitizng solution cornprising a dichromate salt, the solvent of said sensitizing solution consisting essentially of about 10 to -20 volume percent water and the balance of a liquid selected from the group consisting of acetone isopropyl alcohol, methyl alcohol and ethyl alcohol, said treatment enabling said binder to be made water insoluble by subsequent electron bombardment,

(d) drying -said `treated layer,

(e) projecting electrons onto render the binder o f said and portions of said layer to portions insoluble in water,

portions of said layer to portions insoluble in water,

(f) developing said layer in water to remove any portions thereof from said substrate whose binder has not been water insolublized.

8. The method of providing a patterned layer of particles on a substrate, said method comprising the steps of:

(a) depositing on said substrate a layer of a highly dispersed suspension of phosphor particles in an aqueous solution of polyvinyl alcohol binder,

(b) drying said layer,

(c) treating said layer with a sensitizng solution comprising a dichromate salt, the solvent of said sensitizng solvent consisting essentially of about 10 to 20 volume percent water and the balance of a liquid selected from the group consisting of acetone isopropyl alcohol, methyl alcohol and ethyl alcohol, said treatment enabling said binder to be made Water insoluble by subsequent exposure to UV light radiations,

(d) drying said treated layer,

(e) projecting UV light radiations onto portions of said layer to render the binder of said portions insoluble in water, and

(f) developing said layer in Water to remove any portions thereof from said substrate whose binder has not been water insolublized.

9. The method of providing a patterned layer of particles on a substrate, said method comprising the steps of:

(a) depositing on said substrate a layer of a highly dispersed suspension of carbon particles in an aqueous solution of polyvinyl alcohol binder,

(b) drying said layer,

(c) treating said layer with a sensitizng solution oomprising a dichromate salt, the solvent of said sensitizing solvent consisting essentially of about 10 to 20 volume percent water and the balance of a liquid selected from the group consisting of acetone, isopropyl alcohol, Imethyl alcohol and ethyl alcohol, said treatment enabling said binder to be made Water insoluble by subsequent exposure to ultraviolet light,

(d) drying said treated layer,

(e) projecting ultraviolet light onto portions of said layer to render the binder of said portions insoluble in Water, and

(f) developing said layer in water to remove any portions thereof from said substrate whose binder has not been water insolubilized.

References Cited by the Examiner UNITED STATES PATENTS 2,897,089 7/ 1959 Ahlburg 96-35 2,914,404 11/'1959 Fanselau et al. 96-35 3,067,349 12/ 1962 Kasperowicz et al. 117-33 3,095,317 6/1963 Saire 117-335 3,198,634 i 8/1965 Payne 96-35 NORMAN G. TORCHIN, Primary Examiner. A. D. RICCI, C. L. BOWERS, JR., Assistant Examiners. 

1. THE METHOD OF DEPOSITING A LAYER OF PARTICLES ONTO A SUBSTRATE COMPRISING THE STEPS OF: (A) APPLYING TO SAID SUBSTRATE A LAYER OF A MIXTURE INCLUDING SAID PARTICLES AND A BINDER WHICH IS SOLUBLE IN WATER (B) APPLYING TO SAID LAYER A SOLUTION OF SENSITIZER FOR SAID BINDER, THE SOLVENT OF SAID SENSTIZER SOLUTION COMPRISING WATER AND AT LEAST ONE MEMBER OF THE GROUP CONSISTING OF ALCOHOL AND ACETONE THEREBY 